I. Field of the Invention
This invention relates to a heat radiation element, and more particularly to an element including a substrate and a metal oxide layer formed thereon.
II. Description of the Prior Art
A heat radiation element is extensively used in various fields including the use as internal parts of an electron tube, a heating wire, a heat-collecting member, a heat-dissipating member, etc. For example, the anode of a transmitter valve or a receiver valve is struck by thermoelectrons discharged in operation from the cathode, resulting in heating of the anode. If the temperature elevation by the heating is excessive, the gas occluded in the metal constituting the anode is rapidly discharged. Further, the wall of the valve is also heated, leading to a noticeable discharge of the gas occluded in the wall. Still further, thermal deformation is caused by the heating. The drawbacks mentioned combine to invite deterioration in characteristics of the valves and cause undesirable accidents. Accordingly, it is necessary that the anode be made of a material having a good heat radiation property.
Known heat radiation materials include a so-called soothing material, a material containing intermetallic compounds, etc. The sooting material is prepared by depositing soot generated by burning organic substances such as benzene and acetone in the presence of an insufficient amount of oxygen on a substrate of nickel, iron or iron-nickel alloy. The material thus prepared is satisfactory in terms of its heat radiation property. But, difficulties are presented by troublesome production steps which are carried out under difficult working circumstances. In addition, the attachment of the soot to the substrate is relatively weak; the soot is relatively easily removed from the substrate if simply rubbed.
The material containing intermetallic compounds is prepared by the steps of, for example, cladding aluminum on iron and diffusing the aluminum into the iron so as to form black intermetallic compounds on the surface. The material of this type is also satisfactory in its heat radiation property but, because of its low resistance against high temperatures, fails to provide a satisfactory heat radiation element used in a large electron tube.